The production of boards of wooden raw material using wood fibers on the on hand and bicomponent plastic fibers on the other hand is known in the art, for example, from WO 2002/022331 [U.S. Pat. No. 7,405,248]. While conventional methods usually envision the use of thermosetting binders for making boards of a wooden material, such as for example isocyanates, the method that is disclosed in WO 2002/022331 uses bicomponent plastic fibers as a binder that are mixed with the wood fibers; for example, they are spread into a mat via a mechanical strewing head. This mat then is pressed and activated by hot air. The mat is subsequently cooled. In contrast to insulating boards manufactured with thermosetting binders, products of this type have a high level of flexibility, which is necessary, for example, for use as insulation between rafters in order to accommodate the normally encountered tolerances in building applications.
DE 100 56 829 discloses a comparable method of making an insulating board of on the one hand wood fibers and on the other hand thermoactivated plastic fibers. The fiber mixture is spread on an endless mesh belt; this fiber mixture is compacted and/or thickness-adjusted between endless mesh belts, specifically to a thickness of at least 20 mm. The plastic fibers that can be thermally activated are then cross-linked in a hot-air drying tunnel or flow-through dryer downstream to form a matrix that penetrates the wood fibers. During this step, a hot-air treatment at temperatures of approximately 150° C. occurs causing the plastic is outer layer of the bicomponent fibers, for example a polyethylene jacket, to become partially melted, while the plastic core, for example a polypropylene core, has a higher temperature resistance than the polyethylene jacket. The insulating boards that are manufactured in this way should have a volume weight of 20 kg/m3 to 170 kg/m3.
A further method that is known in the art for making wood-fiber insulating boards provides that wood fibers and binding fibers are combined into a fiber mat and the fiber mat is transferred to a kiln conveyor and transported from there through a heating/cooling oven where the softening of the binding fibers and thereby the internal gluing of the wood fibers, takes place. The final thickness of the wood-fiber insulating board of 3 to 350 mm is achieved by calibrating and/or compacting (see DE 10 2004 062 649 [US 2006/0143869]).
Finally, it is known in the art to use a binder belonging to the group of reactive isocyanates, in connection with the conventional production of wood-fiber insulating boards to create a fiber mat, and the mat is compacted to the desired board thickness having a raw density of 40 to 200 kg/m3, preferably 60 to 80 kg/m3, and the fiber mat that has been compacted in such a manner is heated with steam or a steam-air mixture. This steam-air mixture is adjusted and or regulated in terms of its moisture content and temperature in such a way that the binder completely cures while holding the compacted state, and the compacted fiber mat and/or the board-shaped final product has a compensation moisture of 12% without drying process (see DE 102 42 770). The steam-air mixture that is blown into the board provides the temperature of approximately 90° C. that is needed for the setting of the water-free binder, which is achieved by condensation of the steam part in the fiber mat. But such developments did not influence the manufacture of wood-fiber insulating boards with multicomponent plastic fibers. Moreover, DE 196 35 410 discloses a method of and an apparatus for the production of biologically degradable insulating boards comprised of wood and/or plant particles as insulating structural materials and of an environmentally safe binder. Suitable binders for this purpose are, in particular, urea or phenol resins, starches, sugar or polyvinyl acetate, and possible other binders that may be used as additional but also as sole binders are condensation-blended resins, potato pulp, latex and/or protein glues. The starting material is first chipped into a raw material and/or shredded, glued and dried either before or after application of the glue. A fleece is produced from this intermediate material by a spreading method, and in a continual throughput process this fleece is subjected to the following sequential treatment steps: first the fleece is compacted to the desired board thickness and during the following treatment steps the board is maintained at that thickness; second a steam-air mixture is introduced into the compacted fleece over a period of 10 to 20 seconds while avoiding any premature curing of the binder; third a hot-air flow is finally directed through the compacted fleece for the purpose of curing and drying.